1. Field of the Invention
The present invention relates to a communication device, a vehicle-installed system, a communication system, and an anti-theft system, in particular to the same that utilize an ultra wide band (UWB) wireless wave.
2. Description of the Related Art
A UWB wireless system is a wireless system in which communication is carried out by using significantly wide-range frequency-band and narrow pulses of about several GHz or several tens of GHz and less than 1 ns.
FIG. 1 shows a wave shape of transmitted data of the wireless communication system and FIG. 2 shows a frequency band of the wireless communication system. FIG. 1B illustrates the wave shape of PSK (phase sift keying) and FIG. 1A illustrates the wave shape of UWB.
Communication is carried out by generating a narrow-wide pulse, called as an impulse, in a data train that is less than 1 ns. Since the UWB system can avoid the necessity for continuously generating a carrier as in the PSK system shown in FIG. 1B, it requires less power consumption than the communication system in which information is superimposed on a carrier such as PSK.
Further, a narrow pulse, which is used in the UWB system, has good permeability of being able to pass through a wall such as a gypsum-board wall, a wood wall, a concrete wall and others. For this reason, various applications have been examined.
However, since the transmit power is restrained up to a radiation electromagnetic noise limit level in the UWB system, as shown in FIG. 2, there has been no other choice but to shorten the communication distance.
With respect to the prior art, reference may be made to JP08-511341 A, which discloses a radar using the UWB system.
A traditional UWB wireless system has its application area in radar system art. However, since the communication distance is short, application to typical radar system or communication system involves difficulties.
Therefore, it is a general object of the present invention to provide a communication device, a vehicle-installed system, a communication system, and an anti-theft system that can make advantageous use of the characteristics of the UWB communication system.